To meet the demand for wireless data traffic having increased since deployment of 4G (4th-Generation) communication systems, efforts have been made to develop an improved 5G (5th-Generation) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “Security technology” have been demanded for IoT implementation, a sensor network, a Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing Information Technology (IT) and various industrial applications.
In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as a sensor network, Machine Type Communication (MTC), and Machine-to-Machine (M2M) communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud Radio Access Network (RAN) as the above-described Big Data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.
The cellular industry typically operates over licensed spectrum, but the cellular industry is considering operating on unlicensed band in order to meet the surging traffic demands. The unlicensed band is free to be used by any technology, but is governed by few regulations (in most countries) like the requirement of “Listen Before Talk-LBT” which requires a transmitter on the unlicensed band to sense the channel for at least 20 microseconds and if the channel is found to be free (not used by other devices), then the transmitter is allowed to transmit on the unlicensed bands. Further the regulations allow for transmissions up to a maximum time limit and also provide means for giving fairness to the other devices/technologies. The unlicensed bands are typically dominated by Wi-Fi, Bluetooth, ZigBee, WiMAX and other technologies. 3GPP has already decided to customize LTE (Long Term Evolution) standards in the LTE Release 13 for operation on the unlicensed bands and to exist harmoniously with Wi-Fi and other technologies using the unlicensed band.
In the legacy 3GPP LTE systems, multiple carriers can be allocated to a multi-carrier capable UEs (User Equipment) in order to boost the data rates (referred to as carrier aggregation). One of the carriers can be referred to as the primary carrier and the other carriers can be referred to as the secondary carriers. The assumption is that the sub-frame boundaries on all the carriers are aligned. The scheduling can be self-carrier based or cross carrier based. In the self-carrier mode, the PDCCH (Physical Downlink Control Channel) for a secondary carrier is sent on the secondary carrier itself; while in cross carrier mode, the resource allocation for all the secondary carriers is contained in the PDCCH that is sent on the primary carrier only. This is further illustrated in FIG. 1. The eNB (eNodeB) configures measurements for a carrier by indicating the carrier frequency index and by assigning gaps for measurement if required (for example if all the RF chains of the UE are already occupied for data transfer on different carriers. The UE performs the measurements based on the assigned gaps (if configured) and then the UE performs averaging as specified which is designed to filter out the short term channel fading and then when a reporting trigger (for example, the averaged measured value becomes greater than a threshold), the UE reports the measurements to the eNB which based on the reported measurements and its load and other parameters, adds a carrier to the UE. The data transfer is then performed on the added carrier in addition to performing data transfer on the already added carriers. When the average measurement for a carrier goes below a threshold, it is removed (de-configured) from the UE. The UE measures the Cell Specific RS, which is sent by eNB in one symbol of every sub-frame. The UE performs one measurement sample every 40 ms and then averages 5 such samples over 200 ms period and then reports the averaged value if the final averaged value meets a configured reporting trigger.
3GPP has started to work on utilizing the unlicensed bands for cellular communication. It has been agreed to add an unlicensed carrier in the legacy carrier aggregation framework of LTE. The unlicensed carrier is assumed to work in a license assisted manner.
The standalone usage of unlicensed carrier is referred to as LTE-U (LTE-Unlicensed). In LTE-U systems, a carrier that is to be added can be an unlicensed carrier. In order to add the unlicensed carrier, it is essential to perform measurements for the unlicensed carriers, as performed in legacy LTE before the addition of a licensed carrier. But in the LTE-U systems, the eNB cannot guarantee when it can occupy the unlicensed channel and hence the UE cannot know when to measure the unlicensed channel.